Is Noise Trading Cancelled Out by Aggregation?
通过模型分析发现，即使投资者的偏差相互独立，这些偏差仍可能显著影响均衡资产价格，原因包括需求函数的非线性和财富分布波动，导致价格超调等现象。
Conventional wisdom suggests that investors' independent biases should cancel each other out and have little impact on equilibrium at the aggregate level. In contrast to this intuition, this paper analyzes models with biased investors and finds that biases often have a significant impact on the equilibrium even if they are independent across investors. First, independent biases affect the equilibrium asset price if investor demand for the asset is a nonlinear function of the bias. Second, even if the demand function is linear in the bias, it may still have a significant impact on the equilibrium because of the fluctuation of the wealth distribution. An initial run-up of the stock price makes optimistic investors richer, which then further pushes the stock price up and leads to lower future returns. This effect can lead to price overshooting, i.e., a negative expected future return. Similarly, an initial drop of the stock price leads to higher future returns. Simple calibrations show that a modest amount of biases can have a large impact on the equilibrium.